A wild guess would be Fairy Ring Champignon, but I'm no expert, so could be anything.
Marasmius oreades (Blot. ex Fr.) Fr. Fairy Ring Mushrooms, Nelkenschwindling Nymphe des montagnes, Faux Mousseron, Marasme des Oréades Fairy Ring Champignon Fairy Ring Mushroom. Cap 25cm across, convex then flattened with a large broad umbo, tan when moist drying buff tinged with tan at the centre. Stem 20100 x 35mm, whitish to pale buff, tough, rigid. Flesh thick at the centre of the cap, whitish. Smell of fresh sawdust. Gills white then ochre-cream, distant. Spore print white. Spores pip-shaped, 810 x 56um. Cuticular cells smooth, subglobose. Habitat often forming rings in the short grass of pasture or lawns. Season late spring to late autumn. Common. Edible and good. Distribution, America and Europe (From Rogers Mushrooms).